This invention relates to a method for the production of branched fructooligosaccharides which have a specific structure utilizing microorganisms or an enzyme which is produced by microorganisms belonging to the genus Aspergillus using sucrose as raw material.
The physiological activity possessed by fructooligosaccharides has recently become of major interest ["KagaKu to Seibutsu" (Chemistry and Biology), Vol. 21, p. 291]. For example, fructooligosaccharides are difficult to digest and are selectively utilized by useful intestinal flora, Lactobacillus bifidus in particular, thereby promoting proliferation of these organisms and improving laxation and the like. In addition, when broken down by Lactobacillus bifidus, organic acids are produced. These have been recognized to have the effect of reducing cholesterol levels in the body.
Fructooligosaccharides are formed as a result of a fructose transferase (fructosyl transferase) acting on sucrose. Microorganisms that are known to form fructose transferases include yeast, Aspergillus niger, Aureobasidium pullulans, etc. In addition, as has been previously shown by the inventors, fructooligosaccharides can also be effectively produced using fructose transferase produced by Aspergillus sydowi [see TOKKYO-KOKAI-KOHO (18-month Publication of Unexamined Patent Application) SHOWA 61(1986)-187797 (hereinafter referred to as TOKKAISHO 61-187797)].
However, these fructose transferases acted on sucrose and either formed fructooligosaccharides with a structure in which several fructose are linked by .beta.-1,2 bonds to the fructose residue of sucrose, or formed high molecular weight polyfructan composed of the same linkages. Examples of sugars obtained using the fructose transferase produced by microorganisms such as those indicated above and having structures other than these have thus far not been reported.
Conversely, it is known that fructooligosaccharides are produced by various plants ("Kagaku to Seibutsu", Vol. 18, p. 674). It has been reported that non-reducing fructose polymers having a degree of polymerization of 3-15 exist in the storage roots of asparagus in particular, and their structures have been elucidated [N. Shiomi, J. Yamada & M. Izawa, Agric. Biol. Chem., 40, 567 (1976), 43, 1375 (1979), 43, 2233 (1979)]. The fructooligosaccharides found in the storage roots of asparagus have a structure in which fructose is linked at both the glucose residue and fructose residue of sucrose resulting in the structure having a branching form. Fructooligosaccharides having these structures were not found in fructooligosaccharides that are formed using microorganisms.
The purpose of this invention is to provide a method for the production of branched fructooligosaccharides so that naturally-occurring branched fructooligosaccharides, which have heretofore been known only to exist in higher plants, are able to be industrially produced using enzymes of microorganisms.
As was previously stated, although the inventors had shown that fructooligosaccharides such as 1-ketose and nystose, in which fructose is linked by .beta.-1,2 bonds at the fructose residue of sucrose, can be obtained utilizing the mycelia of Aspergillus sydowi, as a result of following research, it was found that branched fructooligosaccharides in which fructose is linked to both the glucose residues and fructose residues of sucrose can be obtained simultaneously with the above fructooligosaccharides under the same reaction conditions, and this has lead to the completion of this invention.